Proteases are involved in a wide variety of biological processes. Disruption of the balance between proteases and protease inhibitors is often associated with pathologic tissue destruction. Indeed, various studies have focused on the role of proteases in tissue injury, and it is thought that the balance between proteases and protease inhibitors is a major determinant in maintaining tissue integrity. Serine proteases from inflammatory cells, including neutrophils, are implicated in various inflammatory disorders, such as pulmonary emphysema, arthritis, atopic dermatitis and psoriasis.
Proteases also appear to function in the spread of certain cancers. Normal cells exist in contact with a complex protein network, called the extracellular matrix (ECM). The ECM is a barrier to cell movement and cancer cells must devise ways to break their attachments, degrade, and move through the ECM in order to metastasize. Proteases are enzymes that degrade other proteins and have long been thought to aid in freeing the tumor cells from their original location by chewing up the ECM. Recent studies have suggested that they may promote cell shape changes and motility through the activation of a protein in the tumor cell membrane called Protease-Activated Receptor-2 (PAR2). This leads to a cascade of intracellular reactions that activates the motility apparatus of the cell. Thus, it is hypothesized that one of the first steps in tumor metastasis is a reorganization of the cell shape, such that it forms a distinct protrusion at one edge facing the direction of migration. The cell then migrates through a blood vessel wall and travels to distal locations, eventually reattaching and forming a metastatic tumor. For example, human prostatic epithelial cells constitutively secrete prostate-specific antigen (PSA), a kallikrein-like serine protease, which is a normal component of the seminal plasma. The protease acts to degrade the extracellular matrix and facilitate invasion of cancerous cells.
Synthetic and natural protease inhibitors have been shown to inhibit tumor promotion in vivo and in vitro. Previous investigations have indicated that certain protease inhibitors belonging to a family of structurally-related proteins classified as serine protease inhibitors or SERPINS, are known to inhibit several proteases including trypsin, cathepsin G, thrombin, and tissue kallikrein, as well as neutrophil elastase. The SERPINS are extremely effective at preventing/suppressing carcinogen-induced transformation in vitro and carcinogenesis in animal model systems. Systemic delivery of purified protease inhibitors apparently reduces joint inflammation and cartilage and bone destruction as well.
Topical administration of protease inhibitors finds use in such conditions as atopic dermatitis, a common form of inflammation of the skin, which may be localized to a few patches or involve large portions of the body. The depigmenting activity of protease inhibitors and their capability to prevent ultraviolet-induced pigmentation have been demonstrated both in vitro and in vivo (See e.g., Paine et al., J. Invest. Dermatol., 116:587-595 [2001]). Protease inhibitors have also been reported to facilitate wound healing. For example, secretory leukocyte protease inhibitor was demonstrated to reverse the tissue destruction and speed the wound healing process when topically applied. In addition, serine protease inhibitors can also help to reduce pain in lupus erythematosus patients (See e.g., U.S. Pat. No. 6,537,968).
As noted above, protease inhibitors interfere with the action of proteases. Naturally occurring protease inhibitors can be found in a variety of foods such as cereal grains (oats, barley, and maize), Brussels sprouts, onion, beetroot, wheat, finger millet, and peanuts. One source of interest is the soybean. The average level of protease inhibitors present in soybeans is around 1.4 percent and 0.6 percent for Kunitz and Bowman-Birk respectively, two of the most important protease inhibitors. Notably, these low levels make it impractical to isolate the natural protease inhibitor for clinical applications.
Thus, there is a need for methods and compositions suitable for the large-scale production of protease inhibitors and their variants. In particular, there remains a need for compositions and methods that reduce and/or eliminate risks associated with blood-borne infectious agents when these proteases are produced in mammalian tissue culture cells.